[tombrossman]

I have heard that setting a very long MX TTL can be helpful if your domain registration is ever hijacked. The idea is that enough resolvers will have the original cached records so you can still receive email (and prove ownership). Anyone have any experience with this?

[jlgaddis]

I've not heard that specific reasoning before but I can believe it -- I've seen MTAs continue to (attempt to) send mail to the "old" MX for several days or even weeks (in a few cases) after the RR (with my "standard" 2d TTL) was updated.

[toast0]

Microsoft Exchange used to cache MX lookups for the life of the process. Which is pretty frustrating, but I think that may have coincided with the ~ 45 day uptime cap, so it wasn't completely awful.